Method and device for operating a switching device

ABSTRACT

A method is disclosed for operating a switching device using at least one electromagnetic drive, which has a displaceable armature for opening and closing at least one main contact of the switching device. According to at least one embodiment of the invention, a modification of the magnetic flux between a first position, when the main contact is deactivated, and a second position, when the main contact is activated, is identified in the electromagnetic drive and a solenoid current of the electromagnetic drive is restricted to a predetermined minimum current value in the second position, if the magnetic flux modification exceeds a predeterminable value. One advantage of at least one embodiment is that an actuation displacement of the armature can be identified as reliable, if an associated modification of the magnetic flux is also measured. The metrological recording of the magnetic flux is contactless.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/EP2005/057075 which has anInternational filing date of Dec. 22, 2005, which designated the UnitedStates of America, the entire contents of each of which are herebyincorporated herein by reference.

FIELD

At least one embodiment the present invention generally relates to amethod for operating a switching device and/or a corresponding device.

BACKGROUND

Switching devices, in particular low voltage switching devices, can beused to switch the current paths between an electrical supply device andloads, and therefore to switch their operating currents. Thus, theswitching device opens and closes current paths, allowing the connectedloads to be safely connected and disconnected.

An electrical low-voltage switching device, such as for example acontactor, a circuit breaker or a compact starter, has one or moreso-called main contacts for switching the conducting paths, which can becontrolled by one or also by a number of control magnets orelectromagnetic drives, in order to switch the current paths. Inprinciple, in this case, the main contacts include a moving contactbridge and fixed contact pieces, to which the loads and the supplydevice are connected. In order to close and open the main contacts, anappropriate connection or disconnection signal is passed to theelectromagnetic drive, in response to which their armatures act on themoving contact bridges in such a way that the latter carry out arelative movement with respect to the fixed contact pieces, and eitherclose or open the current paths to be switched.

Appropriately designed contact surfaces are provided in order to improvethe contact between the contact pieces and the contact bridges at pointsat which the two meet one another. These contact surfaces are composedof materials such as for example silver alloys, which are applied atthese points both to the contact bridge and to the contact pieces, andhave a specific thickness.

As a rule, the electromagnetic drive is designed as a solenoid. Thesolenoid in this case has a plunger coil as excitation coil as well asan armature. For conduction of the magnetic flux, the electromagneticdrive is surrounded by an iron yoke. If a current is now applied to theexcitation coil to switch on the switching device, the armature ispulled into the cylindrical opening of the excitation coil. The movementof the armature that finally actuates a contact slider connectedmechanically to the armature, which in turn moves the contact bridges toclose the main contacts.

A switching device of the kind specified above has a power supply, whichgenerates a low-voltage DC voltage from an alternating input voltage onthe network side in the range from 12 V to 24 V for supplying thesolenoid current to the excitation coil. Typical input voltages on thenetwork side are 230 V at 50 Hz or 110 V at 60 Hz. Newer clocked powersupplies have a broad input voltage range from approximately 100 V to230 V. The power supply can also supply an electronic control unit andan electronic monitoring unit of the switching device with current.

During the switch-on process, i.e. in the period of time of theconnection of the power supply to the excitation coil up to reaching anON position at which the armature is fully drawn in, the currentrequirement of the excitation coil is particularly high. This isexplained by the magnetizing current for establishing the magnetic fieldas well as for the conversion of magnetic energy into mechanical kineticenergy. Were this solenoid current to continue to be provided afterreaching the ON position, the excitation coil would heat up in such amanner that erosion of the excitation coil and thereby a failure of theswitching device would be the result.

For this reason, the solenoid current is restricted to a holdingcurrent, which in comparison to the maximum current is substantiallysmaller during the switch-on process. This can for example be producedby way of a timing circuit which, after a predeterminable time, bringsabout a limiting of the solenoid current by the power supply. Adisadvantage of this solution is that no feedback is obtained about anactual actuation of the electromagnetic drive. It may be that the maincontacts of the switching device are not closed at all by theelectromechanical drive. This could be the case for example if dirt hasaccumulated between the armature and the cylindrical opening of theelectromagnetic drive, and this therefore results in these twocomponents of the electromagnetic drive being jammed.

As an alternative, the ON position can be interrogated by way of one ormore switching contacts, through which the limiting of the solenoidcurrent can then be brought about by the power supply. A disadvantage ofthis solution is that the contacts of the switches may become dirty. Inthis case, as in the case described above, the increased solenoidcurrent would then be supplied again by the power supply with thepossible negative consequences mentioned above.

Fault sources such as these in particular must, however, be avoided forthe safe operation of switching devices, and therefore for protection ofthe load and of the electrical installation.

SUMMARY

At least one embodiment of the present invention identifies suchpotential fault sources, and reacts appropriately to them.

At least one embodiment of the present invention makes possible, at aslight cost, a reliable regulation of the solenoid current and areliable feedback on the fact that the electromechanical drive hascarried out an actuation displacement action.

To this end, according to at least one embodiment of the invention, amodification of the magnetic flux between a first position, when themain contact is deactivated, and a second position, when the maincontact is activated, is identified in the electromagnetic drive and asolenoid current of the electromagnetic drive is restricted to apredeterminable minimum current value in the second position, if themagnetic flux modification exceeds a predeterminable value.

When the switching device is switched on, the armature is drawn into thecylindrical opening of the excitation coil of the electromagnetic drive.By moving the armature, the associated contact slider is also actuated,which in turn displaces the contact bridge for closing the maincontacts. At the same time, by displacing the armature, the magneticfield is modified in the region of the cylindrical opening of theelectromagnetic drive. This modification brings about a change in themagnetic flux, which can then be recorded by a measuring facility. Ifthe magnetic flux modification now exceeds a predeterminable value, thesolenoid current is then restricted to a predeterminable minimum valuefor which the electromagnetic drive remains sufficiently stable in theON position.

The great advantage of this is that an actuation displacement of thearmature can be identified as reliable, if an associated modification ofthe magnetic flux is identified or measured. The measurement of themagnetic flux is contactless. As a result, wear or contamination of theswitching contacts for recording the ON position is avoided.

In a particular embodiment, the magnetic flux modification can beidentified by way of an induction coil. In this case, the coil can befitted as air-core coil in the region of the cylindrical opening of theelectromagnetic drive. As an alternative, the coil can have a slightlylarger diameter when compared to the diameter of the armature. If themeasuring coil is now pushed onto and fastened to the armature, aninduction voltage that is induced by the changing magnetic flux can thenin the case of an actuation of the armature be measured at the wire endsof the coil. This measuring voltage can be compared for example by wayof a comparator to a reference value. The output signal of thecomparator can then be relayed as regulation signal to the power supply.

The particular advantage when using a measuring coil is that only then asufficiently high measuring voltage is induced in the measuring coil,even if the change in the displacement of the armature and in this casethe change in the magnetic flux modification take place in asufficiently fast manner. Thus, during an all too slow actuationdisplacement of the armature such as for example due to contamination ofthe armature, also no sufficient voltage is induced in the measuringcoil. Therefore, also no signal is generated for the regulation of thesolenoid current. This faulty switching behavior can thus be dealt withby a downstream electronic monitoring unit.

As an alternative, the magnetic flux modification can also be identifiedby way of a magnetic sensor, in particular by way of a Hall sensor. Byselecting a Hall sensor with particularly small geometrical dimensions,the magnetic flux modification can be recorded advantageously even underconfined conditions.

In a particularly advantageous embodiment, the electromagnetic drive issupported by at least one permanent magnet. The advantage of such drivesis that in the ON position and in the OFF position, an additionalretaining force is generated on the armature. When switching theelectromagnetic drive supported by the permanent magnet on and off,these additional retaining forces are overcome, which leads to adisplacement of the magnetic flux of the permanent magnet or thepermanent magnets in the magnetic circuit. A modification of themagnetic flux of the permanent magnet or the permanent magnets can thenbe identified or measured with the aid of the measuring devicepreviously mentioned. The advantage of permanent magnet supported drivesis that a creeping process of the initial displacement hardly everoccurs since the permanent magnetic holding force strongly decreases onthe armature after a short path of typically 0.1 mm. Therefore, thearmature displacement on average only varies slightly over the switchingcycles during the switching on and off processes. As a result, thechangeover process takes place suddenly in an advantageous manner sothat in the breaking free period, the displacement of the armature takesplace immediately and with full force compared to the purelyelectromagnetic drives.

In a particularly advantageous embodiment, the magnetic fluxmodification is identified or measured outside an excitation coil andoutside an internal yoke of the electromagnetic drive surrounding theexcitation coil. The iron yoke usually almost completely encloses theexcitation coil except for the cylindrical opening for guiding thearmature so that the magnetic field generated by the excitation coil is,for the most part, formed for the movement of the armature in the regionof the cylindrical opening.

The particular advantage of the above-mentioned arrangement of themeasuring device is that a magnetic flux modification is brought aboutexclusively by a change in the outer permanent magnetic circuit due tothe displacement of the armature. A potentially possible disadvantageousoverlaying of the magnetic flux excited by the permanent magnet by the(electro)magnetic flux generated by the excitation coil is therebyavoided. As a result, from the modification of the magnetic flux of thepermanent magnet or the permanent magnets, an extremely reliable signalcan be generated for the regulation of the solenoid current for theexcitation coil.

In a further embodiment, the magnetic flux modification can beidentified or measured in a scatter field of one of the permanentmagnets, which changes depending on the position of the armature as wellas the associated magnetically conductive components. This is explainedin greater detail in the example of FIG. 2.

In accordance with a further embodiment, an error message is output if,after the expiry of a predeterminable period of time after switching onthe solenoid current, a magnetic flux modification is not identified inthe electromagnetic drive of the switching device. The predeterminableperiod of time can be in the range from 0.2 s to 1 s. If no signal canbe detected by way of the above-mentioned measuring device within thisperiod of time, it can be assumed that the armature has not moved or hasmoved too slowly despite the application of the solenoid current. Thiscan for example be caused by contamination or wear of the mechanicalcomponents of the electromagnetic drive.

A switching device is also disclosed in at least one embodiment forcarrying out the described method in accordance with the invention forswitching loads, with the switching device being a contactor, a circuitbreaker or a compact branch.

The switching device can also have a device corresponding to the methodin accordance with at least one embodiment of the invention forswitching loads, with the switching device being a contactor, a circuitbreaker or a compact branch.

The switching device in particular may be a three-pole switching devicewith three main contacts for switching on and switching off threecurrent paths with a magnetic drive.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention as well as advantageous embodiments thereof will bedescribed in more detail below with reference to the following figures,in which:

FIG. 1 shows a simplified flow diagram of the method in accordance withan embodiment of the invention,

FIG. 2 shows a sectional view through an example embodiment of thedevice in accordance with an embodiment of the invention with apermanent magnet-supported electromagnetic drive,

FIG. 3 shows a force/path diagram in which the force of the respectivecomponents of the electromagnetic drive in accordance with FIG. 2 isplotted over the path between the ON and OFF position,

FIG. 4 shows an example circuit diagram for restricting the solenoidcurrent of the excitation coil in accordance with FIG. 2, and

FIG. 5 shows an example timing curve of the solenoid current as well asthe input voltage of the power supply for the device in accordance withFIG. 2.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

As illustrated in FIG. 1, the two following steps are essentiallycarried out in the method in accordance with an embodiment of theinvention:

-   Step a) Identification of a magnetic flux modification in the    electromagnetic drive between a first position with a switched-off    main contact and a second position with a switched-on main contact,    and-   Step b) restriction of a solenoid current of the electromagnetic    drive to a predeterminable minimum current value in the second    position, if the magnetic flux modification has exceeded a    predeterminable value.

A modification of the magnetic flux is thus only recorded or measured ifthe armature of the electromagnetic drive also moves and, in doing so,changes the magnetic circuit of the electromagnetic drive. Themeasurement of the magnetic flux is contactless.

FIG. 2 shows a sectional view through an example embodiment of thedevice in accordance with the invention with a permanent magnet 8supported electromagnetic drive 1. In the center of the picture anexcitation coil 6 is shown, which is coiled onto a coil form 7. Theexcitation coil 6 for example has two connections for feeding a solenoidcurrent i. The reference symbol u designates the associated coilvoltage. The coil form 7 and the excitation coil 6 form a cylindricalopening OF, in which an armature 10 of the electromagnetic drive 1 canmove. The armature 10 has a cylindrical pin 11 matched with thedimensions of the cylindrical opening OF as well as a stop plate 12fitted to it. In this case, the entire armature 10 is made of aferromagnetic and in particular soft magnetic material such as forexample iron. The coil form 7 and the excitation coil 6 are surroundedby an internal yoke of a soft magnetic material for conduction of themagnetic flux of the magnetic field generated by the excitation coil 7,with a part of the internal yoke 5 extending into the cylindricalopening OF and forming an internal pole 19 there. In the final analysis,the magnetic field generated in such a way only operates only in theregion of the cylindrical opening OF.

In accordance with an embodiment of the invention, a magnetic fluxmodification is identified in the electromagnetic drive 1 between afirst position with a switched-off main contact 15 and a second positionwith a switched-on main contact 15 and a solenoid current i of theelectromagnetic drive 1 is restricted to a predeterminable minimumcurrent value in the second position, if the magnetic flux modificationexceeds a predeterminable value. The flux modification can for examplebe measured by way of a magnetic sensor which is fitted in the startingregion EO of the cylindrical opening OF. For reasons of clarity, themagnetic sensor itself is not shown in the example of FIG. 2.

In accordance with an embodiment of the invention, the electromagneticdrive 1 is supported by at least one permanent magnet 8 so that in theON position and in the OFF position of the electromagnetic drive 1, anadditional retaining force is generated in the armature 10. In thiscase, the permanent magnets 8 are fitted to the exterior of the internalyoke 5 of the electromagnetic drive 1. The magnetic poles of the twopermanent magnets 8 are in each case designated with a reference symbolN and S. The permanent magnets 8 are preferably arranged along theperiphery of the internal yoke 5. Instead of a plurality of permanentmagnets 8, a magnetic ring or circlet can also be used, which ispolarized in such a way that a North Pole N or South Pole S forms on theinside thereof and a South Pole S or North Pole N on the outside. In theexample of FIG. 2, the side facing towards the outside of the permanentmagnets 8 is connected to a pot-shaped soft magnetic outside yoke 4. Theoutside yoke 4 likewise has a cylindrical opening, in which a contactslider 13 is guided. The contact slider 13 can be actuated by way of astop plate 12 of the armature 10 so that a contact bridge 18 connectedto the contact slider 13 can be moved against fixed contact pieces 16 asthe current path. The reference symbol 17 designates the contacts of themain contact 15. A contact spring 14 serves to apply a contacting forceto the contact bridge 18 for closing the main contact 15 if the armature10 is pulled into the cylindrical opening OF during current excitationof the excitation coil 6.

In addition, a reset spring 9 is introduced into the cylindrical openingOF between the internal pole 19 and the cylindrical pin 11 of thearmature 10, which in the currentless condition of the excitation coil6, drives the armature 10 out of the cylindrical opening OF. Thegeometrical dimensions of the cylindrical pin 11 of the armature 10, theexterior of the internal yoke 5 as well as the inside of the outer yoke4 are aligned in such a way that the stop plate 12 of the armature 10 inan excited ON position strikes against the exterior of the internal yoke5 and in the deactivated condition strikes against the inside of theouter yoke 4. In this case, the broken line illustration of the stopplate 12 shows the ON position of the electromagnetic drive 1.

The advantage in the case of such a drive 1 supported by a permanentmagnet 8 is that a creeping of the initial displacement hardly everoccurs in the case of changeover processes since the permanent magneticholding force strongly decreases on the armature 10 after a short pathof typically 0.1 mm. Therefore, the armature displacement on averageonly varies slightly over the switching cycles during the switching onand off processes. As a result, the changeover process takes placesuddenly so that in the breaking free period, the displacement of thearmature 10 occurs immediately and with full force compared to thepurely electromagnetic drives.

In the lower half of FIG. 2, the curve of the magnetic field MF1 due tothe permanent magnet is depicted as a dotted and dashed line for the OFFposition of the electromagnetic drive 1. In the upper half of FIG. 2,for purposes of comparison, the curve of the magnetic field MF2 due tothe permanent magnet 8 is drawn for the ON position of theelectromagnetic drive 1. In the latter case, there is no path with asmall magnetic resistance for the magnetic field MF2 over the outer yoke4, so that inevitably a magnetic scatter field is formed around thespecific permanent magnet 8. In accordance with the invention, amodification of the magnetic flux or the permanent magnets 8 can now beidentified or measured with the aid of the measuring device previouslymentioned.

In accordance with a further embodiment, the magnetic flux modificationcan be identified outside an excitation coil 6 and outside an internalyoke 5 of the electromagnetic drive 1 surrounding the excitation coil 6.For this purpose, in the example of FIG. 2, a measuring coil 2 is coiledaround a limb of the outer yoke 4. Starting at the OFF position, themagnetic flux MF1 flows through the measuring coil 2 in a stationarymanner. If the armature 10 now moves suddenly to the left to the ONposition, the curve of the magnetic flux then also changes suddenly insuch a way that a scatter field MF2 is also formed in accordance withthe illustration of FIG. 2 in the lower region, with the magnetic fluxin the outer yoke 4 disappearing at the same time. This dynamic changein the magnetic flux in the limb of the outer yoke 4 expresses itself inan induction voltage applied to the connections of the measuring coil 2,the peak value of which increases proportionately to the speed at whichthe magnetic flux changes.

The magnetic flux modification can as an alternative or in addition beidentified or measured in a scatter field MF2 of one of the permanentmagnets 8. In this case, in the example of FIG. 2, a magnetic sensor ora Hall sensor 3 is fitted to the outside of the internal yoke 4 and inthe region of the upper permanent magnets. On the basis of the OFFposition of the electromagnetic drive 1, the magnetic flux stretches—asshown in the lower region of FIG. 2—from the North Pole N over the outeryoke 4, further over the stop plate 12 and the cylindrical pin 11 of thearmature 10 into the internal yoke 5 in the initial region EO of thecylindrical opening OF to the South Pole S of the permanent magnet 8.Because the magnetic resistance over these soft magnetic components 4,12, 11, 5 is particularly low, a significant scatter field is not formedaround the permanent magnet 8. In this way, the lateral region aroundthe permanent magnet 8 is thus field-free as far as possible. Therefore,the Hall sensor 3 outputs a measuring signal with a correspondingly lowmeasured value to the magnetic flux. For reasons of clarity, theelectrical connections of the Hall sensor 3 itself are not shown. If thearmature 10 now moves suddenly to the left to the ON position, the curveof the magnetic flux then also changes suddenly in such a way that ascatter field MF2 is formed, with the magnetic flux in the outer yoke 4disappearing at the same time. A part of the scatter field MF2 now alsoflows through the Hall sensor 3, which now in addition indicates acorrespondingly high measured value.

FIG. 3 shows a force/path diagram in which the force F of the respectivecomponents 9, 10, 19 of the electromagnetic drive in accordance withFIG. 2 is plotted over the path S between the ON position ON and the OFFposition OFF. KBP designates the contact point. Starting from this pointKBP, the contact spring force sets in from the ON position ON. This isshown by the associated characteristic curve KLF. A cause for this isthat starting from this point, the stop plate 12 in its movement fromleft to right in accordance with FIG. 2, hits the contact slider 13, andthen takes it along. The limit stop of the contact slider 13 isrepresented by a broken line at this point KBP in the example of FIG. 2.A spring resetting force works against the contact spring forceaccording to the characteristic KLR, which decreases with an increasingpath of the armature 10 towards the OFF position OFF. The characteristicKLO shows the curve that depends on the distance of the force in thearmature 10 in the case of an electromagnetic drive without forcesupport by permanent magnets 8. As shown in FIG. 3, the force of thereset spring 9 still acting on the contact bridge 18 is relativelysmall. On the other hand, the characteristic KLS when compared to thecharacteristic KLR shows an increasing force determined by the magneticflux setting in now over the outer yoke 5 in accordance with FIG. 2, ifthe armature 10 moves towards the OFF position OFF.

FIG. 4 shows an example circuit diagram for restricting the solenoidcurrent i of the excitation coil 6 in accordance with FIG. 2. In theleft part of FIG. 4, a rectifier 21 is represented, which converts an ACvoltage AC on the input side into a DC voltage US. This DC voltage US issubsequently supplied to a stepdown controller by way of a controllableelectronic switching element 22, which in turn feeds the excitation coil28 of the electronic drive in accordance with FIG. 2 with the solenoidcurrent i. In this case, a voltage u_(E) is applied to the electronicswitching element 22, which depending on the switching state of theswitching element 22 corresponds to the switching voltage US or avoltage value close to 0 V. In the closed state of the switching element22, a load inductance 24 is loaded via the rectifier 21. In the openstate of the switching element 22, a freewheeling diode 26 relays thesolenoid current i. An example resistor 23 serves as a measuringresistor for recording the actual current i, with a proportionatelysmall current flow through a filter condenser 27 able to be ignored. udesignates the voltage over the excitation coil 28. In the right part ofFIG. 4, a measuring coil 29 can be seen, in which a voltage u_(i) isinduced during a flux modification of the magnetic field in theelectromagnetic drive. This induction voltage u_(i), together with ameasuring voltage u_(R), which is proportional to the solenoid currenti, is recorded and processed by an electronic control unit 25.

When a switching-on command ON is given, the electronic control unit 25now first of all makes available a high solenoid current i, so that thearmature 10 can be moved safely from the OFF position OFF to the ONposition ON. The breaking free of the armature 10 from the OFF positionOFF, brings about a magnetic flux modification. The electronic controlunit 25 now records a sufficiently high pulsed voltage u_(i) and then ina regulating loop restricts the solenoid current i to a predeterminableminimum current value. To this end, the control unit 25 activates theelectronic switching element 22 in a clocked manner.

FIG. 5 shows an example curve in time of the solenoid current i as wellas the input voltage u_(E) of the power supply for the device inaccordance with FIG. 2. The voltage curve KLU of the input voltage u_(E)is plotted in the lower part of the time diagram and the current pathKLI of the solenoid current i in the upper part. At the point in timet0, the control unit 25 in accordance with FIG. 4 receives, aswitching-on command ON, whereupon this control unit then first of allconnects the switching voltage US in full. At the point in time t1, thearmature 10 breaks free from the outer yoke 5, whereby a regulationsignal in the form of an induced voltage signal u_(i) is generated inthe measuring coil 29 in accordance with FIG. 4. As a result, thecontrol unit 25 regulates the solenoid current i in such a way that itfluctuates between the two current changeover values IO and IL and onaverage corresponds to an averaged current value IL.

Example embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the present invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

1. A method for operating a switching device using at least oneelectromagnetic drive, which includes a displaceable armature foropening and closing at least one main contact of the switching device,the method comprising: identifying a magnetic flux modification in acylindrical opening formed between an excitation coil and a coil form ofthe electromagnetic drive by identifying a change in an outer permanentmagnetic due to displacement of a movable armature within thecylindrical opening, the magnetic flux modification occurring due to achange between a first position with a switched-off main contact of theelectromagnetic drive and a second position with a switched-on maincontact of the electromagnetic drive; and restricting a solenoid currentof the electromagnetic drive to a certain current value in the secondposition, when the magnetic flux modification exceeds a threshold valuewherein an error message is output if, after the expiry of a period oftime after switching on the solenoid current, a magnetic fluxmodification is not identified in the electromagnetic drive of theswitching device.
 2. The method as claimed in claim 1, wherein themagnetic flux modification is identified by way of an induction coil. 3.The method as claimed in claim 2, wherein the magnetic flux modificationis identified by way of a magnetic sensor.
 4. The method as claimed inclaim 1, wherein the magnetic flux modification is identified by way ofa magnetic sensor.
 5. The method as claimed in claim 4, wherein themagnetic sensor is a Hall sensor.
 6. The method as claimed in claim 1,wherein the electromagnetic drive is at least supported by one permanentmagnet; and the magnetic flux modification is identified in a magneticcircuit of the at least one permanent magnet.
 7. The method as claimedin claim 6, wherein the magnetic flux modification is identified outsidethe excitation coil and outside an internal yoke of the electromagneticdrive surrounding the excitation coil.
 8. The method as claimed in claim7, wherein the magnetic flux modification is identified in a scatterfield of one of the permanent magnets.
 9. A switching device forcarrying out the method for switching loads as claimed in claim 1,wherein the switching device is at least one of a contactor, a circuitbreaker and a compact branch.
 10. A switching device as claimed in claim9, wherein the switching device is a three-pole switching device withthree main contacts for switching on and switching off three currentpaths with a magnetic drive.
 11. The method as claimed in claim 1,wherein the certain current value is a predeterminable minimum currentvalue.
 12. A device for operating a switching device using at least oneelectromagnetic drive, the device comprising: an excitation coil woundon a coil form within an internal yoke, the excitation coil and the coilform forming a cylindrical opening therein, wherein a portion of theinternal yoke extends into the cylindrical opening formed by theexcitation coil and the coil form; a displaceable armature for openingand closing a main contact of the switching device, the displaceablearmature being moveable within the cylindrical opening the armatureincluding a cylindrical pin within the cylindrical opening, thecylindrical pin being connected to a contact bridge; an identifyingdevice that identifies a magnetic flux modification in the cylindricalopening when the contact bridge moves between a first position, when amain contact is deactivated, and a second position, when the maincontact is activated; and a restricting device that restricts a solenoidcurrent of the electromagnetic drive to a certain current value in thesecond position, when the magnetic flux modification exceeds a thresholdvalue wherein an error message is output if, after the expiry of aperiod of time after switching on the solenoid current, a magnetic fluxmodification is not identified in the electromagnetic drive of theswitching device.
 13. The device as claimed in claim 12, wherein thatthe identifying device includes at least one of an induction coil and amagnetic sensor.
 14. The device as claimed in claim 13, wherein themagnetic sensor is a Hall sensor.
 15. The device as claimed in claim 12,further including at least one permanent magnet fitted to an exteriorsurface of the inner yoke and provided to support the electromagneticdrive, the permanent magnet proving an additional retaining force to thecylindrical pin, wherein the magnetic flux modification in thecylindrical opening is identified by a change in the permanent magnet.16. The device as claimed in claim 15, wherein the identifying device isarranged outside the excitation coil and outside the internal yoke ofthe electromagnetic drive surrounding the excitation coil.
 17. Thedevice as claimed in claim 12, wherein an error message is outputtableif after the expiry of a period of time after switching on the solenoidcurrent, a magnetic flux modification cannot be identified in theelectromagnetic drive of the switching device.
 18. A switching devicefor switching loads with a device as claimed in claim 12, wherein theswitching device is at least one of a contactor, a circuit breaker and acompact branch.
 19. The device as claimed in claim 12, wherein thecertain current value is a predeterminable minimum current value.
 20. Adevice for operating a switching device using at least oneelectromagnetic drive, which has a displaceable armature for opening andclosing a main contact of the switching device, comprising: anexcitation coil wound on a coil form, the excitation coil and the coilform forming a cylindrical opening therein; an internal yoke withinwhich the excitation coil and the coil formed are arranged, a portion ofthe internal yoke extending into the cylindrical forming an internalpole therein; a cylindrical pin within the cylindrical opening, thecylindrical pin being connected to a contact bridge; an identifyingdevice that identifies a magnetic flux modification in the cylindricalopening when the electromagnetic drive moves between a first position,when a main contact is deactivated, and a second position, when the maincontact is activated; and a restricting device that restricts a solenoidcurrent of the electromagnetic drive to a certain current value in thesecond position, if the at least one device identifies that the magneticflux modification exceeds a threshold value wherein an error message isoutput if, after the expiry of a period of time after switching on thesolenoid current, a magnetic flux modification is not identified in theelectromagnetic drive of the switching device.